When applications require large amounts of storage, many hard drives or other data storage devices are combined together, for example, disk arrays or RAID (Redundant Array of Independent Disks) arrays. These use multiple drives combined for increased storage, better performance, or greater reliability.
When data is written to the drive, magnetic interference can cause the data in nearby sections to become weaker or be destroyed. To reduce the loss of data, disks use background processes, which continuously scan the disk and check for data issues that could lead to the contained information becoming unrecoverable. For example, a section of data that is repeatedly re-written can cause electrical charge interference to adjacent tracks. In another example, a block of data can become unreadable either due to a physical obstruction on the disk, damage from impact, or damage due to normal use of the disk.
A known method of protecting hard drives, in order to increase the reliability and longevity of the drive, is to use S.M.A.R.T. (Self-Monitoring, Analysis, and Reporting Technology) technology. S.M.A.R.T. measures crucial parameters such as operating temperature, spin-up time, and data error rates. Certain trends and sudden changes in these parameters are thought to be associated with increased likelihood of drive failure and data loss.
Another known method for protecting disks is background scrubbing or scanning, where the hard disk controller reads through the entire disk and checks for errors. If an error is found, the error is corrected using either a backup of the data, or a parity check to determine the piece of data that is corrupted or missing. In general, this process individually corrects errors before they compound, which can generate more severe or uncorrectable errors.